Biology Reference
In-Depth Information
(ii)
Dmrt
: The minireview of Herpin and Schartl (2011) summarizes
information thus far gathered on the early gonadal differentiation in
a dozen gonochoric fi sh. Of fi ve genes, gonad specifi c expression has
been found for
Dmrt1
in many species,
Dmrt2
in
O. latipes
(Winkler et
al., 2004),
Dmrt3
in
D. rerio
(Li et al., 2008),
Dmrt4
in
O. aureus
(Cao et
al., 2010),
O. latipes
(Winkler et al., 2004),
Paralichthys olivaceus
(Wen
et al., 2009) and
Dmrt 5
in
D. rerio
(Guo et al., 2004). Interestingly,
Dmrt4
and
Dmrt1
are predominantly expressed in the ovary and
testis of
O. aureus,
respectively. They have been sub-cloned into the
vector pMAL-c2x and introduced into the
Escherichia coli
TB1 cell for
effi cient fusion. After purifi cation and cleavage, Dmrt4
and Dmrt1
proteins have been used to immunize adult rabbits. Western blot
analysis has shown that these
Dmrt4
and
Dmrt1
have become highly
specifi c and are expressed only in the ovary and testis, respectively
(Cao et al., 2007). Male restricted expression has been shown in
O.
latipes, X. maculatus, P. olivaceus, O. niloticus, Gobiocypris rarus
and
Clarias gariepinus
(Table 11). A strong male-biased expression has been
found in
O. mykiss, D. rerio, Takifugu rubripes, Gadus morhua, Acipenser
fulvescens, Scaphirhynchus platorhynchus
and
Silurus meridionalis.
When
detected in the ovary, the expression of
Dmrt1
is specifi c to germ
cells alone in
G. morhua
and
D. rerio.
Two distinct DM domain DNAs
tDMRT1
from the testis and
tDMO
from the ovary are isolated in
O. niloticus
. A male specifi c motif is absent in
tDMO.
The alternatively
spliced male and female types of
double sex tDmrt-1
and
tDMO
cDNAs
are encoded by two different genes. The mutually exclusive nature of
tDmrt-1
and
tDMO
expression in the testis and ovary indicates that
they both play an important role in gonad development and function.
In vitro
(promoter analysis) studies have revealed that
Dmrt1
inhibits
transcriptional activity of
cyp19a1a
and
Double sex and Mab-3
domain
is essential to repress basal as well as
Ad4BP/SF-1-
activated
cyp19a1a
in HEK 293 cells. Immunohistochemical analysis has shown that the
transgenic overexpression of
Dmrt1
in XX tilapia down- regulated
cyp19a1a
expression, decreased aromatase expression reduced serum
estradiol 17β levels, retardation of the formation of ovarian cavity
induced varying degrees of follicular degeneration and even a partial
or complete sex reversal (Wang et al., 2010).
In
S. meridionalis
too,
Dmrt1a
expresses in the testis but
Dmrt1b
in the ovary (Liu Z et al.,
2007). In
Clarias gariepinus,
Raghuveer and Senthilkumaran (2009)
have found two alternative spliced forms of
Dmrt1
. They code for
proteins with 287 (
Dmrt
), 253 (
Dmrt1a
) and 233 (
Dmrt1b
) amino acid
residues and are localized in spermatogonia and spermatocytes. The
potential role of
Dmrt1
in testicular differentiation, as evidenced
